Studies on the mechanism of action of m-AMSA (NSC-141549) were extended to include a comparison of the effects of m-AMSA with those of the microsomal metabolites of m-AMSA with regard to toxicity, DNA-binding, and induction of single-strand DNA breaks. 5-Fluorodeoxyuridine-5'-methylphosphonate, an analog of FdUMP designed to circuvent FUdR resistance, was synthesized and biologic evaluation initiated. Two analogs of Actinomycin D were synthesized and evaluated for biologic effects.